The invention relates generally to the field of embedding and extracting hidden messages in source data. This field is also referred to as data hiding, information hiding, watermarking and also steganography. More specifically the invention relates to the generation of a dispersed message for embedding in a digital image in a camera or printer.
U.S. Pat. No. 6,044,156 issued Mar. 28, 2000 to Honsinger et al. entitled Method For Generating An Improved Carrier For Use In An Image Data Embedding Application, discloses a technique for embedding messages in digital image data. This method for embedding a hidden message into a digitized image includes the steps of: forming a digitized version of the desired message; generating a random phase carrier; convolving the digitized version of the desired message and the random phase carrier to form a dispersed message; and combining the dispersed message with the digitized image to form an embedded hidden message image. Hidden messages may be embedded in photographic images recorded on film and paper using conventional photographic printing techniques, or they may be embedded in images produced on printers such as ink jet and thermal dye transfer printers, by combining the dispersed message with a digital image using digital image processing techniques.
The hidden messages are recovered from the embedded hidden message image by cross correlating the embedded hidden message image containing the dispersed message with a decoding carrier to recover the embedded dispersed message; and extracting the digital message data from the recovered dispersed message.
One problem with the above described techniques is that when a digital image is formed in an apparatus such as a camera or a printer, the complex computer processing capability needed for forming the dispersed message is not present in the apparatus although the apparatus will generally include a simple computer suitable for basic digital image processing and machine control. There is a need therefore for a simpler method of forming the dispersed message.
The need is met according to the present invention by providing a method for forming a dispersed message for embedding in an image, that includes the steps of: providing a random phase carrier; defining a set of ordered bit locations; assigning a polarity to each bit location corresponding to a bit of the message; cyclically shifting the random phase carrier in accordance with each bit location and weighting the cyclically shifted carriers by the polarity of the corresponding bit; and forming a sum of the cyclically shifted weighted carriers to form the dispersed message.
The method of the present invention has the advantage of requiring very little image processing capability for implementation, and is therefore suitable for use in apparatus such a digital camera or printer.